Electric switch with magnetic-assist means to assist switch in closing and remaining closed against high currents

ABSTRACT

An electric switch includes magnetic-assist means for assisting the switch in closing and remaining closed against high currents. The magnetic-assist means develops a magnetic force acting in a switch-closing direction, even when the switch contacts are substantially fully separated. A toggle-type linkage connected between the magnetic-assist means and the movable contact of the switch limits to a relatively low value the portion of the magnetic force transmitted to the movable contact until the movable contact has passed through a substantial portion of its closing stroke.

United States Patent 11 1 Kroon Dec. 4, 1973 15 ELECTRIC SWITCH WITH 3,319,121 5 1967 Lee 317 12 R MAGNETIC ASSIST MEANS o ASSIST 3,366,900 1/ 1968 Barkan 335/15 3,663,906 5 1972 Barkan et al. 335 195 SWITCH IN CLOSING AND REMAINING CLOSED AGAINST I-IIGII CURRENTS Appl. No.2 308,155

US. Cl. 335/16 Int. Cl. H0lh 77/10 Field of Search 335/16, 15, 195,

References Cited UNITED STATES PATENTS 6/1952 Scott, Jr 335/16 Primary Examinerl-Iarold Broome Att0rney-.l. Wesley Haubner et a].

[5 7 ABSTRACT An electric switch includes magnetic-assist means for assisting the switch in closing and remaining closed against high currents. The magnetic-assist means develops a magnetic force acting in a switch-closing direction, even when the switch contacts are substantially fully separated. A toggle-type linkage connected between the magnetic-assist means and the movable contact of the switch limits to a relatively low value the portion of the magnetic force transmitted to the movable contact until the movable contact has passed through a substantial portion of its closing stroke.

11 Claims, 4 Drawing Figures PATENTEDBEE 4 1975 SHEET 2 [IF 3 PATEMEUBEE 3,777,291

' sum 3 or 3 r 1 ELECTRIC SWITCH WITH MAGNETIC-ASSIST MEANS TO ASSIST SWITCH IN CLOSING AND REMAINING CLOSED AGAINST HIGH CURRENTS BACKGROUND This invention relates to an electric switch that includes magnetic-assist. means to assist the switch in closing and in remaining closed against high currents and, more particularly, relates to magnetic-assist means that is especially adapted for use in a switch in which high currents can flow therethrough at the start of or during the early stages of a closing operation, even though the switch is in or near its fully-open position.

When high current flows through the engaged contacts of a typical switch, high magnetic forces are developed that tend to force the contacts apart. As explained in more detail in U.S. Pat. No. 3,225,160- Barkan, assigned to the assignee of the present invention, these forces result primarily from the tendency of the current path to restrict at the point of contact engagement and, thus, to develop loop-shaped components, each comprising arms extending along confronting faces of the contacts. Current through these loopshaped components creates a repulsive, contactseparating force between the arms of each loop. These contact-separating forces, which are referred to hereinafter as contact-popping forces, vary directly with the square of the current and, hence, can be very high when currents of short circuit magnitude pass through the engaged contacts.

For opposing these contact-popping forces developed when high currents pass through the engaged contacts, various electromagneticv arrangements have been devised which act on the contacts to hold them engaged with a force also varying directly with the square of the current through the contacts. In certain of these electromagnetic arrangements, referred to hereinafter as magnetic-assist arrangements, a currentdependent magnetic force is developed and applied to the movable contact in a switch-closing direction whenever current flows through the contacts, irrespective of contact position at the time current begins flowing. Generally speaking, however, this magnetic-assist force is not needed unless the. contacts are engaged, or

just about to engage, at the end of a closing stroke. It

is only when the contacts are engaged that the high contact-popping forces are developed. If magneticassist force proportional to the square of short circuit current is applied to the contacts-during the entire closing stroke, there is a tendency to produce unpredictable and unduly high'closing speeds.

In most switches, the development of the magneticassist force is automatically delayed until the 'instant needed inasmuch as no current flows through the contacts during a closing stroke until the contactsengage or are about to engage at the end of the closing stroke. This automatic delay, however, is not present in the switch application that thepresent invention is concerned with. In this particular switch application, the switch has triggering means which is operable to cause current to flow between the contacts even when they are in or near their fully-separated position. An example of this type of switch application is illustrated in U.S. Pat. No. 3,319,12l-Lee, assigned to the assignee of the present invention.

SUMMARY A general object of my invention is to provide magnetic-assist means which is especially adapted for use in a switch application in which current can flow through the switch contacts at the start of or during the early stages of a switch-closing operation, even when the contacts are in or near their fully-separated position.

Another object is to provide magnetic-assist means which, though it develops a force varying directly with current magnitude when the contacts are fullyseparated, is controlled in such a manner that only a small portion of said force acts in a closing direction on the movable contact of the switch when the movable contact is in or near its fully-separated position.

Another object is to provide means for rapidly accelerating the movable contact in a closing direction at the start of the closing stroke which provides an accelerating force that is independent of current magnitude and which is ineffective to oppose high-speed opening motion at the start of a subsequent opening stroke.

Another object is to construct the magnetic-assist means in such a manner that a single magnetic-assist means can serve to hold closed the contacts of two separate circuit interrupters against the high contactpopping forces developed when a high current flows through the two interrupters.

In carrying out my invention in one form, I provide an electric switch that comprises a first contact, a second contact that is movable into and out of engagement with the first contact, and triggering means operable to cause current to flow between said contacts while the contacts are substantially fully separated and during substantially an entire closing stroke. The switch further comprises magnetic-assist means for developing for transmission to said second contact a magnetic force acting in a switch-closing direction which varies directly in accordance with the current through said contacts. Means is provided for transmitting said magnetic force from said magnetic-assist means to the second contact which includes means for limiting to a relatively low value the portion of the magnetic force transmitted when the contacts are in and near their fullyseparated position but transmitting a relatively large portion when said contacts are in and near their fully closed position. Spring means controlled by a suitable latch is provided for biasing the second contact toward closed position when the contacts are fully separated .and the latch is released.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is a side elevational view, partly in section and partly schematic, showing a switch embodying one form of my invention.

FIG. 2 is a schematic side elevational view of switchoperating means constituting a part of the switch of FIG. 1. In FIG. 2 the switch is depicted in its fully-open position.

FIG. 3 shows the switch-operating means of FIG. 2 in a position through which it passes at an intermediate point in a switch-closing operation.

FIG. 4 shows the switch-operating means of FIG. 2 in the position it occupies when the switch is fully closed.

i Triggered Interrupters l4 and I Referring now to FIG. 1, the switch shown therein comprises a stationary housing 12 for the "operating mechanism of the switch and two vacuum-type circuit interrupters l4 and 15 fixed to opposite sides of the housing.

Each vacuum interrupter is a triggered vacuum interrupter of a general type shown and claimed in the above-mentioned U.S. Pat. No. 3,319,121-Lee. As such, each interrupter comprises a sealed envelope 16 that is evacuated to a pressure of 10 4 tort or lower. The envelope 16 comprises a cylindrical casing 18 of a suitable insulating material and a pair of metallic end caps 20 and 21 at opposite ends of the casing. Suitable seals 22 are provided between the end caps and the casing to provide a vacuum-tight joint between these parts.

Located within each evacuated envelope -16 is a pair of main electrodes 24 and 25 that are normally spaced apart to define a main or primary gap 26 located therebetween. Electrode 24 is a stationary electrode which is supported on the outer end plate 20 by means of stationary supporting rod 24a; whereas electrode 25 is a movable electrode which is joined to and carried by an elongated conductive operating rod 25a that projects through an opening in the inner end plate 21. A flexible metallic bellows 27 is provided about operating rod 25a to permit vertical movement thereof without impairing the vacuum inside envelope l6. Bellows 27 is secured by suitable seals at its respective opposite ends to operating rod 25a and end plate 21.

For each interrupter, a stationary guide 23 is provided for slidably receiving the movable contact rod 25a and thereby guiding it for motion along a straight line vertical path.

Under normal conditions, there is a high voltage present between main electrodes 24 and 25, but no current flows therebetween since the main gap 26 normally has sufficient dielectric strength to withstand this voltage without breakdown.

For causing the main gap 26 tobreak down in response to predetermined conditions, there is provided a trigger electrode (schematically shown at 30) suitably insulated from main electrode 24. Between this trigger electrode 30 and main electrode 24, there is atrigger gap which is sparked over when a predetermined voltage is applied between the trigger electrode and the main electrode. The resulting sparkover produces ionized vapors which are rapidly injected into the main gap 26 to reduce its dielectric strength, thus allowing the voltage that is then present between the main electrodes 24 and 25 immediately to produce an arc-over of the main gap 26. Reference may be had to the aforesaid Lee patent for a more detailed description of the trigger gap and its mode of operation.

Operating Mechanism 2 To prevent the electrodes 24 and 25 from being damaged by the above-described arc-over and to provide a solid metallic path through the switch, the movable electrode 25 is rapidly driven'into engagement-with stationary electrode 24 immediately following are-over.

The force for producing this closing motion of elec- I trode 25 is developed by an operating mechanism3'5 (shown in FIG. 2) located within housing 12. The operating-mechanism "is a stored-energy type device, operationofwhich is initiated by ieleasing a suitable latch or restraining means (shown schematically at 36 in FIG. 2) coupled to the operating mechanism through a vertically-extending control rod 37 of insulating material. The illustrated latch 36 iscontrolled by a solenoid 38 which is adapted to be energized in response to current flow of a predetermined value between the main electrodes 24, 25 thereby releasing the latch and allowing the operating mechanism 35 to operate.

Referring now to FIG. 2, the operating mechanism 35 comprises two sub-assemblies of substantially identical construction, only one of which, the lower subassembly, will be described in detail. This sub-assembly comprises a compression spring 40 which is coupled to a crank 42 which, in turn, is coupled to movable contact rod 25a through a connecting link 44. Compression spring 40 is located within a cylinder 46 and bears at one end against the rear wall of the cylinder and at its opposite end against a piston-like guide member 48 slidably mounted in the cylinder. Guide member 48 contains a centrally-located hole in which one end ofa push rod 50 is slidably mounted. Push rod 50 is pivotly connected at its opposite end to the crank 42 by a pivot pin 52 and has a shoulder 54 thereon against which guide member 48 bears when the parts are in the position of FIG. 1.

Crank 42 is pivotally mounted on a stationary pivot 55 and is coupled to the connecting link 44 through a pivot pin 56. Intermediate its ends, the connecting link 44 is pivotally connected to contact rod 25a through a pivot 58; and at one end, the connecting link 44 is pivotally connected at 60 to a main toggle link 62. Toggle link 62 is pivotally mounted on a stationary pivot 64 and is coupled to the vertically-extending control rod 37 through a linkage comprising a crank 68 and a tension member 70. Crank 68 is pivotally mounted on a stationary pivot 71 and has one arm pivotally connected at 69 to control rod 37 and its other arm pivotally connected at 73 to tension member 70. Tension member 70 is pivotally connected to toggle link 62 through the pin and slot connection comprising a pin 72 on a toggle link and a slot 74 in the tension member It will be apparent from the above that when the parts are in the position of FIGS. 1 and 2 the compression spring 40, acting through elements 50, 42, and 44 is biasing the movable contact rod 25a in a downward closing direction but is restrained from so moving the contact rod by latch 36 (FIG. 1) acting through the parts62, 70, 68, and 37 to hold these latter parts in their illustrated position. When the latch 36 is released, parts 62, 70, 68, and 37 are no longer so restrained, and the compression spring 40 is thus free to drive movable contact. rod 25a in a closing direction. Compression spring 40 continues this driving action until its guide member 48 encounters a stationary buffer 76 on the cylinder 46. When this occurs, the inertia of the moving parts (with certain assistance, soon to be described) continues the closing operation, carrying the parts throughtheir position of FIG. 3 into their fully-closed position of FIG."4.

A suitable'conventional dashpot 79 acts near the end of theclosing stroke to decelerate the mechanism and limit the contact velocity on impact to the desired rangeQThis dashpot does not significantly affect opening speeds.

Magnetic-Assist Means 80 When the contacts first touch at the end of a closing stroke, magnetic forces (referred to herein as contactpopping forces) proportional to the square of the current are abruptly established, which forces act in a direction to drive the contacts apart and oppose the force tending to hold them closed. These contact-popping forces are explained in more'detailin the introductory portion of this application. Typically, the switchwill be closed against very high currents, and thus extremely high contact-popping forces are developed at or near the end of the closing stroke.

For overcoming these high contact-popping forces, magnetic-assist means 80 is provided. This magneticassist means comprises two identical bars 81 of electroconductive materialwhich are electrically connected in series with each other and with the contacts of the two interrupters. For connecting the two bars 81 in series with each other, a flexible conductive braid 83 is connected between the adjacent right hand ends of the bars. Additional braid 84 is provided at the left hand end of each bar, and each of these braids 84 is electrically connected to its associated movable contact rod a by means of a'conductor schematically shown at 85. Each of the bars 81 is mounted on a stationary pivot pin 86. When current flows through the bars 81 via the interconnecting braid 83, it passes in opposite directions through the bars; and this results in a magnetic repulsive force being developed therebetween tending to force the bars apart by pivoting them in opposite angular directions about their associated pivots 86.

Toggles Linkages 90, 62 and 92, 62

The force developed by magnetic assist means 80 is transmitted to the movable contact rod 25a of each interrupter by linkage means comprising two toggle links 90 and 92, which come into play sequentially, as will soon be described. Referring to the lower subassembly, the first toggle link 90 is pivotally connected'at its lower end to previously-described main toggle link 62 by a pivot pin 93 andis pivotally connected at its upper end to the bar 81 through a pin and slot connection 94, 95. The second toggle link 92 is pivotally connected at its lower end to the main toggle link 62 and is pivotally connected at its upper end to the bar. 81 by means of a pin and slot connection 96, 97.

When the parts are in a position of FIG. 2, the first toggle link90 and the main toggle link 62 are relied upon for transmitting force from the magnetic-assist means 80 to the movable'contact rod 25a. The second toggle link 92 is then inactive. But when the closing operation has reached the point depicted in FIG. 3, the first toggle link 90 drops out of play and the second toggle link 92 comes into play. To explain this more specifically with reference to the lower sub-assembly, when the parts are in the position of FIG. 2, the magneticassist means 80 forces the pin 94 downwardly against the bottom of slot 95in link.90, thus transmitting force from magnetic-assist means 80 through link 90. This driving relationship at 94, 95 continues while the parts are moving through a closing stroke from their position of FIG. 2 to that of FIG. 3; but when the parts pass beyond their position of FIG. 3 toward their position of FIG. 4, the lower wall of slot 95 of link 90 moves out of engagement with pin 94, thus interrupting the previ ously-existing driving relationship at 94, 95.

During the above-described closing motion that carried the parts between their positions of FIG. 2 and FIG. 3, no driving force was transmitted through second toggle link 92 because pin 96 remained spaced from the bottom of slot 97 in the second toggle link. But when the parts entered their position of FIG. 3, the bottom of slot 97 and pin 96 engage, and thereafter force from the magnetic-assist means 80 is transmitted to main toggle link 62 through the second toggle link 92 While the parts are in their position of FIG. 2 and while moving between their positions of FIGS. 2 and 3, the links 90 and 62 are acting as a toggle, the knee of which is the pin 93 which joins links 90 and 62. This toggle is substantially on center when in the position of FIG. 2 inasmuch as knee pin 93 is located on the toggle center line 100 interconnecting the axes of pins 64 and 94. The knee 93 moves away from center line 100 as the parts move in a closing direction toward their position of FIG. 3. As a result of the initial on-center relationship of toggle 90, 62, the magnetic-assist forces are substantially completely blocked and no substantial force is applied to the main toggle links 62 in a direction to rotate it. But as the toggle 90, 62 moves off center toward its position of FIG. 3, the toggle 90, 62 becomes progressively more capable of rotating link 62 in a counterclockwise closing direction. When the position of FIG. 3 is reached, the toggle 90, 62 becomes ineffective, as abovedescribed; and a new toggle, formed by links 92, 62 and knee pin 93 and having a center line 102, becomes effective. In the position of FIG. 3, toggle 92, 62 is very close to, or even slightly under, dead center, and thus the effectiveness with which closing forces are transmitted from the magnetic-assist means to the main toggle lever 62 is again at a very low level. After continued closing motion, however, toggle knee 93 moves across and then progressively further away from the toggle center line 102, thus rendering toggle 92,.62 progressively more effective in transmitting closing force from the magnetic assist means 80 to main toggle link 62. Note in FIG. 4 the relatively large distance then present between the toggle knee 93 and center line 102, resulting in relatively great effectiveness of the toggle when transmitting closing and hold-closed forces to the contact rod 25a.

Functions of Toggle Linkages It will be apparent from the above description of toggles 90, 62 and 92, 62 that they cooperate to limit to a low level the closing force transmitted from magnetic-assist device 80 to movable contact rod 25a until near the end of the closing stroke. One of my reasons for limiting this force until near the end of the closing stroke is that high magnetic closing force is needed only when the contacts are in or very near engagement since this is the only time when high contact-popping forces, which tend to separate the contacts, are developed. Another reason is that I desire to minimize the variations in closing speed resulting from the different values of magnetic force developed by the magneticassist means 80. In this respect, it should be noted that the repulsive force developed between the two bars 81 of the magnetic-assist device is directly dependent upon the level of current flowing there through. In a triggered interrupting device such as I am dealing with, current flowis initiated while the interrupter is still fully open, and thus this current-dependent repulsive force between bars 81 is developed while the switch is still fully open. If this repulsive force was transmitted without reduction to the movable contact rod 25a,

variations therein would have a much more pronounced effect on closing speed than occurs in my -arrangement, where only a small portion of this repulsive force is transmitted to the movable contact rod during the early stages of closing. In my arrangement, the force for initial closing motion is supplied principally by closing spring 40, and this is a force that is independent of current variations. In other words, the total closing force during the first portion of a closing action comprises a large current-independent major component (from spring 40) and another component-that, though current dependent, is held to a minor and relatively insignificant value in relationship to the total by the toggle action described hereinabove.

In certain applications of my switch, it is very desirable that the contacts 24, 25 reach engagement at an instant near current zero of the alternating current wave. It is much easier to achieve this result if the closing speed is predictable and not subject to major variations as a result of differences in current. Since my closing speed during much of the closing stroke is not drastically affected by current variations, as has been pointed out above, I am able to provide a more predictable closing speed that enables me to more consistently reach contact-engagement near current zero.

A factor which contributes to the effectiveness of the toggle 92, 62 in transmitting closing force to the movable contact when the contacts are in their engaged position of FIG. 4 is the mechanical advantage that it provides in transmitting force from the magnetic-assist device 80 to the contact rod 25a. In this regard, not that when the switch is in its closed position of FIG. 4, the force from the magnetic-assist device is transmitted along the path of an arrow 105. The effective lever arm of this force path, as measured from stationary pivot 64 to the arrow 105 normal thereto, is considerably greater than the distance betweenpivots 60 and 64. This results in a mechanical advantage equal to the ratio of the longer to the shorter lever arm, thus enabling a given repulsive force developed in the magnetic-assist device to exert a considerably larger force on center, as well as from the fact that the interrupting devices l4 and 15, being of the vacuum type, have very short strokes.

Other Features It is to be noted that the closing spring 40, in driving the operating mechanism during the early portion of the closing operation, does not dissipate any of its energy in accelerating the relatively massive parts of the magnetic-assist device 80. In this regard, the slots 95 and 97 in the toggle links 90 and 92 permit these parts 90, 92 to be driven by the closing spring free of the bars 81. The bars are moved in follow-up relationship to these links and 92 by the above-described repulsive magnetic force between the bars 81 and also by auxiliary closing springs 110, soon tobe'described.

The auxiliary closing springs serve also tohold the contacts of the interrupters in engagement under light-current or no-current conditions when they are standing in engagement. These auxiliary closing springs are shown as tension springs, each connected between a stationary point and a pin 96 on one of the bars 81. Under light current or no current conditions, little or no hold-closed force is developed by the magneticassist device; but the auxiliary springs 110 provide a hold-closed force that assures that the contacts will remain in engagement with sufficient contact pressure until the mechanism is deliberately operated in an opening direction.

When each of the movable contacts 25 engages its stationary contact at the end of a closing stroke, the latching linkage 70, 68, 37, which had been moving in follow-up relationship to the main toggle link 62, continues moving in the same direction for a short additional distance, driven primarily by a follow-up spring 114 connected to the vertical rod 37. This added motion moves each of the two tension members 70 further to the left into the position of FIG. 4, as permitted by the slot 74 in each tension member 70 sliding on pin 72. Finally, the latching linkage 70, 68, 37 encounters a suitable stop (not shown) which terminates its motion. The slotted connections 74, 72 permit the two movable contacts 25 to seat independently of each other without restraint from the latching linkage 70, 68, 37 and its stop.

For opening the switch, an opening operator such as the solenoid schematically shown at 115 in FIG. 1 is provided. This solenoid, when energized, drives the contact rod 37 downwardly from its closed position (not shown) into its open position of FIG. 1, where the control rod 37 is then held by latch 36. During the early part of such opening motion, the slotted portion 74 of each tension member 70 slides over the pin 72, imparting no opening force to the associated movable contact 25 until the left hand end of the slot 74 impacts against the pin 72. This impact is applied through links 70, 62, 44 to the contact rod 25a and serves the desirable function of breaking any welds that might then be present between the contacts. Further motion of the linkage 70, 68, 37 carries the movable contact 25 through its opening stroke.

In the circuit applications in which my switch is applied, opening is effected only when there is a relatively low current through the contacts. This means that the magnetic-assist means 80 is not then developing a high force opposing contact separation, thus enabling a solenoid 115 of reasonable size to be used for producing opening.

Another factor that reduces the force requirements imposed on the opening solenoid 115 during the opening operation is the fact that the closing spring 40 does not oppose initial opening action since it was snubbed by stop 76 during the preceding closing action well before the closing stroke was completed. As a result, during the'opening operation the push rod 50 is able to move through travel depicted at in FIG. 4 before the closing spring (40) begins to exert any opposition to the opening action.

It is to be noted that in the disclosed operating means there are virtually no mechanisms or actuators which require resetting between the endof an opening stroke and the start of a closing stroke. Closing can commence as soon as the movable contacts 25 has reached its fully-open position and the latch 36 (of FIG. 1) is tripped. Likewise, opening can occur as soon as the contacts reach their closed position of FIG. 4.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects, and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new'and desire to secure by Letters Patent of the United States is:

1. An electric switch comprising:

a. a first contact and a second contact that'is movable into and out of engagement with said first contact,

b. triggering means operable to cause current to flow between said contacts while said contacts are substantially fully-separated,

c. magnetic-assist means for developing for transmission to said second contact a magnetic force acting in a switch-closing direction which varies directly in accordance with the current through said contacts,

d. means for transmitting said magnetic force from said magnetic-assist means to said second contact comprising means for limiting to a relatively low value the portion of the magnetic force transmitted when said contacts are in and near their fullyseparated position but transmitting to said second contact a relatively large portion of said magnetic force when said contacts are in and near their fullyclosed position,

e. spring means biasing said second contact toward closed position when said contacts are fully separated, and

f. releasable restraining means for holding said second contact in said fully-separated position against the bias of said spring means and releasable to permit said spring means to drive said second contact toward engaged position.

2. The switch of claim 1 in which:

a. said spring means comprises a closing spring that discharges during the early stages of a switchclosing operation to accelerate said second contact in a switch-closing direction, and

b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point atwhich said contactsengage during a switch-closing operation.

3. The switch of claim 1 in which:

a. said means for limiting the force transmitted from said magnetic assist means comprises a toggle linkage connected between said magnetic-assist means and said second contact which operates near an oncenter position when said second contact is near its fully-separated position,

b. said toggle linkage having a portion serving as an output end duringv a closing operation through which forces from said magnetic-assist'means are transmitted to said movable contact,

c. the toggle linkage being so constructed that the portion of the input force transmitted therethrough to said output end is relatively low when said toggle linkage is operating near its on-center position compared to that portion transmitted when the toggle linkage is operating further away from its oncenter position. I

4. The switch of claim 1 in which:

a. said means for limiting the force transmitted from said magnetic-assist means to said second contact comprises first and second toggle linkages, both of which are connected between said magnetic-assist means and said second contact,

b. said first toggle linkage being effective to transmit force from said magnetic-assist means to said second contact when said contacts are near their fullyseparated position,

c. said second toggle linkage being ineffective to transmit force from said magnetic-assist means to said second contact when said contacts are near their fully-separated position,

d. means operable after the first stages of a switchclosing operation for rendering said first toggle linkage ineffective and said second toggle linkage effective to transmit force from said magneticassist means to said second contact,

e. said second toggle linkage operating near its oncenter position when it first becomes effective and operating further away from said on-center position as the switch-closing operation progresses,

f. said second toggle linkage having a portion serving as an output end during a switch closing operation through which forces from said magnetic-assist means are transmitted to said movable contact,

g. said second toggle linkage being so constructed that the portion of the input force transmitted therethrough to said output end is relatively low when said second toggle linkage is operating near its on-center position compared to that portion transmitted when said second toggle linkage is operating further away from its on-center position.

5. The switch of claim 4 in which said first toggle linkage is substantially on-center when said contacts are fully separated and remains near center duringthe closing operation until said second toggle linkage becomes effective, said first toggle linkage having a portion serving as an output end during a closing operation through which forces from said magnetic-assist means are transmitted to said movable contact when said first toggle linkage is effective, and said first toggle linkage being so constructed that the portion of the input force transmitted therethrough to said output end of the first toggle linkage is relatively low when said first toggle linkage is operating near its on-center position compared to that which would be transmitted to said toggle linkage if the toggle linkage were operating further away from its on-center position.

6. The switch of claim 3 in which:

a. said spring means comprises a closing spring that discharges during the early stages of a switchclosing operation to accelerate said second contact in a switch-closing direction, and

b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point at which said contacts en gage during a switch-closing operation.

7. The switch of claim 4 in which:

a. said spring means comprises a closing spring that discharges during the early stages of a switchclosing operation to accelerate said second contact in a switch-closing direction, and

b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point at which said contacts engage during a switch-closing operation.

8. The switch of claim in which:

a. said spring means comprises a closing spring that discharges during the early stages of a switchclosing operation to accelerate said second contact in a switch-closing direction, and

b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point at which said contacts engage during a switch-closing operation.

9. The switch of claim 1 in which:

a. said magnetic-assist means comprises two side-byside bars electrically connected in series with said contacts in such a manner that current at any instant flows in opposite directions through said bars to develop a repulsive magnetic force therebetween that drives one of said bars in a switchclosing direction,

b. and said means for transmitting said magnetic force is connected between said one bar and said second contact.

10. In the switch of claim 1,

a. a second set of contacts comprising a first contact and a second contact that is movable into and out of engagement with said first contact,

b. additional triggering means operable substantially simultaneously with triggering means of claim 1 to cause current to flow between the contacts of said second set while the contacts of said second set are substantially fully separated,

c. means for connecting both sets of contacts in series so that current flows inseries therethrough when both said triggering means are operated,

d. the electromagnetic assist means of claim 1 being common to the two sets of contacts and being connected in series with said two sets of contacts to develop responsive to current flow therethrough a second magnetic force acting in a switch-closing direction on the movable contact of said second set of contacts, I

e. means corresponding to the force transmitting means of (d) of claim 1 for transmitting said second magnetic force to the second contact of said second set,

f., second spring means biasing the second contact of said second set toward closed position when the contacts of said second set are fully separated, and

g. the releasable means of (f) of claim 1 also holding the second contact of said second set in its fullyseparated position and, upon release, permitting said second spring means to drive said second contact of said second set toward engaged position.

11. The switch of claim 10 in which said magneticassist means comprises two side-by-side bars through which current at any instant flows in opposite directions to develop a repulsive effect therebetween that produces said two magnetic forces, one of said forcetransmitting' means being connected between one of said bars and one of said second contacts, and the other of said force-transmitting means being connected between the other of said bars and the other of said second contacts. 

1. An electric switch comprising: a. a first contact and a second contact that is movable into and out of engagement with said first contact, b. triggering means operable to cause current to flow between said contacts while said contacts are substantially fullyseparated, c. magnetic-assist means for developing for transmission to said second contact a magnetic force acting in a switch-closing direction which varies directly in accordance with the current through said contacts, d. means for transmitting said magnetic force from said magnetic-assist means to said second contact comprising means for limiting to a relatively low value the portion of the magnetic force transmitted when said contacts are in and near their fully-separated position but transmitting to said second contact a relatively large portion of said magnetic force when said contacts are in and near their fully-closed position, e. spring means biasing said second contact toward closed position when said contacts are fully separated, and f. releasable restraining means for holding said second contact in said fully-separated position against the bias of said spring means and releasable to permit said spring means to drive said second contact toward engaged position.
 2. The switch of claim 1 in which: a. said spring means comprises a closing spring that discharges during the early stages of a switch-closing operation to accelerate said second contact in a switch-closing direction, and b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point at which said contacts engage during a switch-closing operation.
 3. The switch of claim 1 in which: a. said means for limiting the force transmitted from said magnetic assist means comprises a toggle linkage connected between said magnetic-assist means and said second contact which operates near an on-center position when said second contact is near its fully-separated position, b. said toggle linkage having a portion serving as an output end during a closing operation through which forces from said magnetic-assist means are transmitted to said movable contact, c. the toggle linkage being so constructed that the portion of the input force transmitted therethrough to said output end is relatively low when said toggle linkage is operating near its on-center position compared to that portion transmitted when the toggle linkage is operating further away from its on-center position.
 4. The switch of claim 1 in which: a. said means for limiting the force transmitted from said magnetic-assist means to said second contact comprises first and second toggle linkages, both of which are connEcted between said magnetic-assist means and said second contact, b. said first toggle linkage being effective to transmit force from said magnetic-assist means to said second contact when said contacts are near their fully-separated position, c. said second toggle linkage being ineffective to transmit force from said magnetic-assist means to said second contact when said contacts are near their fully-separated position, d. means operable after the first stages of a switch-closing operation for rendering said first toggle linkage ineffective and said second toggle linkage effective to transmit force from said magnetic-assist means to said second contact, e. said second toggle linkage operating near its on-center position when it first becomes effective and operating further away from said on-center position as the switch-closing operation progresses, f. said second toggle linkage having a portion serving as an output end during a switch-closing operation through which forces from said magnetic-assist means are transmitted to said movable contact, g. said second toggle linkage being so constructed that the portion of the input force transmitted therethrough to said output end is relatively low when said second toggle linkage is operating near its on-center position compared to that portion transmitted when said second toggle linkage is operating further away from its on-center position.
 5. The switch of claim 4 in which said first toggle linkage is substantially on-center when said contacts are fully separated and remains near center during the closing operation until said second toggle linkage becomes effective, said first toggle linkage having a portion serving as an output end during a closing operation through which forces from said magnetic-assist means are transmitted to said movable contact when said first toggle linkage is effective, and said first toggle linkage being so constructed that the portion of the input force transmitted therethrough to said output end of the first toggle linkage is relatively low when said first toggle linkage is operating near its on-center position compared to that which would be transmitted to said toggle linkage if the toggle linkage were operating further away from its on-center position.
 6. The switch of claim 3 in which: a. said spring means comprises a closing spring that discharges during the early stages of a switch-closing operation to accelerate said second contact in a switch-closing direction, and b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point at which said contacts engage during a switch-closing operation.
 7. The switch of claim 4 in which: a. said spring means comprises a closing spring that discharges during the early stages of a switch-closing operation to accelerate said second contact in a switch-closing direction, and b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point at which said contacts engage during a switch-closing operation.
 8. The switch of claim 5 in which: a. said spring means comprises a closing spring that discharges during the early stages of a switch-closing operation to accelerate said second contact in a switch-closing direction, and b. snubbing means is provided for blocking said spring from further discharging at a point substantially ahead of the point at which said contacts engage during a switch-closing operation.
 9. The switch of claim 1 in which: a. said magnetic-assist means comprises two side-by-side bars electrically connected in series with said contacts in such a manner that current at any instant flows in opposite directions through said bars to develop a repulsive magnetic force therebetween that drives one of said bars in a switch-closing direction, b. and said means for transmitting said magnetic force is connected between said one bar and said second contacT.
 10. In the switch of claim 1, a. a second set of contacts comprising a first contact and a second contact that is movable into and out of engagement with said first contact, b. additional triggering means operable substantially simultaneously with triggering means of claim 1 to cause current to flow between the contacts of said second set while the contacts of said second set are substantially fully separated, c. means for connecting both sets of contacts in series so that current flows in series therethrough when both said triggering means are operated, d. the electromagnetic assist means of claim 1 being common to the two sets of contacts and being connected in series with said two sets of contacts to develop responsive to current flow therethrough a second magnetic force acting in a switch-closing direction on the movable contact of said second set of contacts, e. means corresponding to the force transmitting means of (d) of claim 1 for transmitting said second magnetic force to the second contact of said second set, f. second spring means biasing the second contact of said second set toward closed position when the contacts of said second set are fully separated, and g. the releasable means of (f) of claim 1 also holding the second contact of said second set in its fully-separated position and, upon release, permitting said second spring means to drive said second contact of said second set toward engaged position.
 11. The switch of claim 10 in which said magnetic-assist means comprises two side-by-side bars through which current at any instant flows in opposite directions to develop a repulsive effect therebetween that produces said two magnetic forces, one of said force-transmitting means being connected between one of said bars and one of said second contacts, and the other of said force-transmitting means being connected between the other of said bars and the other of said second contacts. 